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Bill Bryson has made some interesting comments about the Rev. Thomas Bayes—comments repeated in two of his recent bestsellers and in this speech before the Royal Society of London—but they may leave a misleading impression.

Curiously, Bryson says that Bayes’ theorem had “no practical applications at all in his own lifetime.” In fact, Bayes’ theorem was not published until two years after his death so it is pretty obvious that it did not have applications before.

Bryson also describes Bayes’ theorem as “very complex” while it is actually a very simple one-liner. It does has two steps though. And Bayes’ starting-off point was the key that the French mathematician Laplace needed to produce the modern version of Bayes’ rule.

Bryson’s most serious misreading of the history of the subject is that Bayes’ theorem was just “an interesting but pointless exercise” until the advent of “very powerful computers.”

In fact, the great English mathematician Alan Turing developed pencil-and-paper Bayes to break the German Navy’s Enigma codes that told U-boats where to find and sink Allied merchant marine ships supplying Britain during World War II.

As Turing’s wartime assistant Jack Good said, Turing may not have won the war for Britain, but without Turing, Britain could have lost the war.

Important elements of Turing’s paper-and-pencil Bayes were also embedded in the pioneering computers that Britain built to decode German Army messages during the war. According to General Dwight Eisenhower, British decoding shortened the war in Europe by two years.

After the war that he helped win, Turing was arrested for homosexual activity in the privacy of his home with a consenting adult. He was convicted and sentenced to chemical castration and committed suicide in 1954.

Turing’s use of paper-and-pencil Bayesian methods are described in my book The Theory That Would Not Die—along with numerous other examples of its paper-and-pencil use in Great Britain, France, Russia, and the United States long before computers.